WaterFurnace Envision2 NXW Chiller - Manual (Page 23)

23
ENVISION 2 NXW REVERSIBLE CHILLER INSTALLATION MANUAL
Control Features cont.
• When the controlling temperature sensor is set to
select the Load LW Temp, the setpoint control will
operate strictly in a proportional mode with offsets and
differentials used to determine the appropriate capacity
to use. In this mode, the following parameters are used:
• Stage Delay (30)
• Gain (2)
• PIDY1 Ref (7.2)
• PID Y1 Diff (7)
• PID Y2RefShift (5)
• PID Y2 Diff (6)
• The default values were used in the test lab and
seem to be a reasonably good beginning point for
parameter settings.
Compressor Lead-Lag Operation
In the Maint menu of the MUI, Lead –Lag operation may be
enabled or disabled. When disabled, a Y1 call will always be
a request for compressor 1 and a Y2 call will be a request for
compressor 2. When Lead-Lag is enabled, the operation is
as follows:
• If only a single Y call is introduced (either Y1 or Y2),
then one compressor will start and it will be the
compressor that has been Off the longest. When
that call is removed, the compressor will stop—if the
compressor minimum run time has been satisfied.
• If the single Y call is re-introduced, then the ‘other’
compressor will start. In this manner, if single
compressor operation is used, then each time a call is
given, the compressors will alternate.
• If a Y call is existing and a compressor is running,
then adding a second Y call will bring on the second
compressor. When one of the Y calls is dropped and
the other remains, then the compressor that was first
started will be dropped. In this manner, if the chiller
is alternating between one and two compressor
operation, both compressors will be cycled.
• If no Y calls exist and a sudden and simultaneous
application of both Y1 and Y2 occur, then fist the
‘longest off’ compressor will start. After 150 seconds,
the second compressor will start.